Contemporary screening methods for prostate cancer have resulted in an increase in the proportion of men detected with low- to intermediate-risk disease, and a decrease in the average age of detection, compared to previous decades. Unfortunately, current detection methods largely based on biopsy, sample less than 1% of the volume of the prostate and provide little information about the exact location and size of the cancer within the gland. As a result, treatments for localized prostate cancer target the entire prostate gland, which is effective at eliminating disease, but leaves many men with long-term complications to sexual, urinary, and bowel function. Diagnostic imaging with MRI has advanced in recent years to the point where it is possible to see the location and size of tumours within the prostate gland. In addition, the development of new ways to treat prostate cancer under image-guidance offer the promise of more precise treatments with the potential for reduced complications. In this proposal, the ability of MRI-controlled transurethral ultrasound therapy to treat localized prostate cancer will be evaluated. This technology involves treatment (through high temperatures) of specified regions in the prostate gland using high-intensity ultrasound energy delivered from a device inserted into the urethra. The unique feature of this treatment is that it is performed entirely within a magnetic resonance imager, which provides non-invasive images of the temperature within the prostate during heating. This integration of heating and temperature monitoring enables very precise treatment of tissue within the gland. The overall goal of this research is to transform the treatment of localized prostate cancer into a minimally- invasive, outpatient procedure that is as effective as current treatments, but has much lower complications associated with it. The goal of this proposal will be to evaluate the ability of MRI-controlled transurethral ultrasound therapy to effectively treat localized prostate cancer detected with diagnostic MRI. This study will be performed in men scheduled for surgery, so their prostate glands can be studied after removal to evaluate the effectiveness of the treatment. This study design is necessary to ensure a safe evaluation of this novel technology which was tested recently for the first time in humans by our group. If successful, the proposed study will demonstrate the ability of this technology to be used to treat prostate cancer effectively, paving the way for future studies comparing this technology with existing treatments for localized prostate cancer.